Estimates for projections in Banach spaces and existence of direct complements
Gunther Dirr, Vladimir Rakočević, Harald K. Wimmer (2005)
Studia Mathematica
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Let W and L be complementary subspaces of a Banach space X and let P(W,L) denote the projection on W along L. We obtain a sufficient condition for a subspace M of X to be complementary to W and we derive estimates for the norm of P(W,L) - P(W,M).